Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $80.93   6.594%   $86.2665   $86.27   $86.25   $86.30  
  Purchase #2 $159.66   11.432%   $177.9123   $177.91   $177.90   $177.90  
  Purchase #3 $178.34   11.633%   $199.0863   $199.09   $199.10   $199.10  
  Purchase #4 $131.53   12.281%   $147.6832   $147.68   $147.70   $147.70  
  Purchase #5 $186.60   7.198%   $200.0315   $200.03   $200.05   $200.00  
  Purchase #6 $200.86   11.107%   $223.1695   $223.17   $223.15   $223.20  
  Purchase #7 $23.92   3.450%   $24.7452   $24.75   $24.75   $24.70  
  7 purchase totals = $961.84       $1,058.8945   $1,058.90   $1,058.90   $1,058.90